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rtc: Fix the AltCentury value on AMD/Hygon platform

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When using following operations:
date -s "21190910 19:20:00"
hwclock -w
to change date from 2019 to 2119 for test, it will fail on Hygon
Dhyana and AMD Zen CPUs, while the same operations run ok on Intel i7
platform.

MC146818 driver use function mc146818_set_time() to set register
RTC_FREQ_SELECT(RTC_REG_A)'s bit4-bit6 field which means divider stage
reset value on Intel platform to 0x7.

While AMD/Hygon RTC_REG_A(0Ah)'s bit4 is defined as DV0 [Reference]:
DV0 = 0 selects Bank 0, DV0 = 1 selects Bank 1. Bit5-bit6 is defined
as reserved.

DV0 is set to 1, it will select Bank 1, which will disable AltCentury
register(0x32) access. As UEFI pass acpi_gbl_FADT.century 0x32
(AltCentury), the CMOS write will be failed on code:
CMOS_WRITE(century, acpi_gbl_FADT.century).

Correct RTC_REG_A bank select bit(DV0) to 0 on AMD/Hygon CPUs, it will
enable AltCentury(0x32) register writing and finally setup century as
expected.

Test results on Intel i7, AMD EPYC(17h) and Hygon machine show that it
works as expected.
Compiling for sparc64 and alpha architectures are passed.

Reference:
https://www.amd.com/system/files/TechDocs/51192_Bolton_FCH_RRG.pdf
section: 3.13 Real Time Clock (RTC)

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Jinke Fan <fanjinke@hygon.cn>
Link: https://lore.kernel.org/r/20191105083943.115320-1-fanjinke@hygon.cn
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
This commit is contained in:
Jinke Fan 2019-11-05 16:39:43 +08:00 committed by Alexandre Belloni
parent afe19a7ae8
commit 7ad295d519
1 changed files with 14 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
drivers/rtc/rtc-mc146818-lib.c
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@ -172,7 +172,20 @@ int mc146818_set_time(struct rtc_time *time)
save_control = CMOS_READ(RTC_CONTROL);
CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
#ifdef CONFIG_X86
if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
boot_cpu_data.x86 == 0x17) ||
boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
CMOS_WRITE((save_freq_select & (~RTC_DIV_RESET2)),
RTC_FREQ_SELECT);
save_freq_select &= ~RTC_DIV_RESET2;
} else
CMOS_WRITE((save_freq_select | RTC_DIV_RESET2),
RTC_FREQ_SELECT);
#else
CMOS_WRITE((save_freq_select | RTC_DIV_RESET2), RTC_FREQ_SELECT);
#endif
#ifdef CONFIG_MACH_DECSTATION
CMOS_WRITE(real_yrs, RTC_DEC_YEAR);